1. Field of the Invention
The present invention relates generally to fabrication of micro-lenses and arrays of micro-lenses and other microscopic structures having curved surfaces. As such the invention related generally to optics, materials science and micro-level manufacturing.
2. Related Art
Micro-Electro-Mechanical Systems (MEMS) are devices which integrate microscopic scale components on a common substrate. Digital mirror devices are one example of a MEMS device that has achieved market success as used within projection televisions.
Fabrication of MEMS devices is sometimes referred to as micromachining. Micromachining can be performed using integrated circuit (IC) processing sequences such as photolithography to define features on a substrate. Silicon is a popular substrate material. Typically, the features manufacturing in photolithography are substantially planar, with deposited or removed layers of material being only a few micrometers thick and generally of uniform thickness. Features are for the most part defined by vertical boundaries, although slopes can be achieved using, for example, directional (non-isotropic) etching (e.g., potassium hydroxide etching of silicon).
There is a desire to produce components within MEMS devices that have a non-planar surface topography. For example, integrated optical systems use micro-lenses or micro-mirrors having diameters between about 1 micrometer to several hundred micrometers. Fabricating curved surfaces of a micro-lens or micro-mirror can be particularly difficult. Some success has been achieved with so-called gray scale lithography, however gray scale masks can be expensive and the photolithography process must be tightly controlled.
Alternate approaches for fabricating non-planar surface in a MEMS device include molding desired features into a polymer material. Long term stability and reliability of polymer material can be a concern.